1. Technical Field of the Invention
The present invention relates generally to a magnetic recording/reproduction apparatus, and more particularly to an improved structure of a magnetic recording/reproduction apparatus designed to record and reproduce digital information on and from a magnetic tape for an extended period of time at a reduced error rate.
2. Background of Related Art
A helical scan magnetic recording/reproduction apparatus is known in the art which is designed to record and reproduce information signals on and from a magnetic tape which is wrapped helically about a rotary drum over a 180.degree. angular range and is moving at a constant speed using two magnetic heads installed on the rotary drum 180.degree. apart from each other. This type of magnetic recording/reproduction apparatus usually uses two magnetic heads to write recording tracks close to each other at different azimuth angles without a guard band or with a considerably narrow guard band for improving the packing density.
Japanese Patent Second Publication No. 6-18047 teaches a helical scan magnetic recording/reproduction system designed to record digital information on a magnetic tape traveling at a speed of one-third of a normal recording speed using a rotary drum (head) spinning (rotating) at the same speed as that in a normal recording three times a normal recording time. The rotary drum has mounted thereon two rotary heads which are diametrically opposed and show different azimuth angles. The rotary heads alternately write slant tracks on the magnetic tape, one every 1.5 rotation of the rotary drum. This achieves azimuth recording for an extended period of time that is an odd multiple of a normal recording time.
In the above system, if only the tape travel speed is changed to half that in the normal recording mode in order to achieve recording for an extended period of time that is an even multiple of the normal recording time, an information signal is recorded on the magnetic tape one time every rotation of the rotary drum. Specifically, the recording of the information signal is achieved by only one of the two rotary heads, thereby resulting in the same azimuth angle in all tracks. This makes it impossible to achieve reproduction utilizing the azimuth loss effect. In order to avoid this problem, a two-channel recording is known which uses an additional rotary head for recording for an extended period of time that is an even multiple of the normal recording time. Additionally, Japanese Patent First Publication No. 6-325305 teaches the use of an additional head for intermittent recording at an azimuth angle which is different from that of one of normal heads.
The recording of data at a recording data rate that is half that in a normal recording mode can also be accomplished at a rotational speed of a rotary drum and a travel speed of a magnetic tape which are half those in the normal recording mode, respectively. In this case, the reproduction is achieved by setting the rotational speed of the rotary drum equal to that in the normal recording mode and the travel speed of the magnetic tape to half that in the normal recording mode.
Accordingly, the two-channel recording/reproduction requires two separate systems: a recording system (a modulator, a recording amplifier, and etc.) and a reproduction system (a ereproduction amplifier, an equalizer, a phase lock loop for data clock playback, and etc.), thus resulting in an increase in production cost.
Further, the odd multiple time recording can be achieved by two rotary heads that are diametrically opposed at the same level, however, the even multiple time recording requires double azimuth heads which show different azimuth angles and which are mounted at different height levels, instead of one of the rotary heads used in the odd multiple recording. This results in complex height adjustment of the rotary heads and an increase in production cost.
The digital data recorders can usually record data of about 14 Mbps for five hours in a normal play mode. However, even 7-Mbps data recording requires addition of dummy data to the original to change the data rate to about 14 Mbps. It is, thus, difficult to prolong a recording time of five hours further. The conventional recording/reproduction system designed to record digital information on a magnetic tape traveling at a speed that is half that in a normal recording mode, wrapped around a rotary drum spinning at a rotational speed that is also half in the normal recording mode and to establish digital reproduction at the rotary drum speed equal to that in the normal recording mode and the tape travel speed that is half that in the normal recording mode, can achieve an about ten-hour recording when the recording data rate is 7 Mbps. In this system, however, scan paths of the rotary heads during reproduction are undesirably shifted from tracks written on the magnetic tape, thereby leading to deterioration in error rate of reproduced data.